SYDNEY coach John Longmire has pleaded with his players to not react to umpiring decisions after two were penalised for dissent during last week's loss to Melbourne.

Umpire dissent returned to the agenda in round three after Greater Western Sydney veteran Stephen Coniglio was penalised for questioning an on-field ruling at a pivotal moment of his side's loss to Carlton.

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On Sunday, Swans players Will Hayward and Chad Warner both gave away free kicks away for dissent in the first quarter as Melbourne started faster at the MCG.

Hayward's outburst marched the Demons upfield, where Lachie Hunter parlayed the 50-metre penalty into a goal and a 15-point lead.

Hayward told Longmire he had been directing his frustrations at a player and not the umpire, but the coach has nonetheless sent a clear message to his players this week.

"It's too big a penalty, 50 metres is a big penalty so don't do it," he said.

"After a decision has been made, you've got to get on with it.

"We'll work on what we can control but as I said to Will, don't say it to the player. Just move on with it.

"The AFL have already come out and made it very, very clear that you can't say anything.

"If it's right, if a decision's right, I understand it. If it's on the borderline, it's a big penalty."

The Swans host Port Adelaide at the SCG this Saturday and will be looking to overcome a poor recent record against the Power, who have won all of the sides' past six meetings.

Only nine members of Sydney's 44-man squad were on the books in 2016 when the Swans last beat Port Adelaide.

"We haven't been consistent for four quarters against them. That's our challenge," Longmire said.

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"You have those things (slumps) against different teams at different times.

"People throw up different things - you can't do this and you can't do that and you've got a record like this - I don't really spend a lot of time in that space.

"You sort of look at the things you can control and focus on that.

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"With this team, this group now, this week, that's the most important thing."

No other side in the competition is on a current streak of more than one win against the Swans.